Cement and cement composition having improved rheological properties

ABSTRACT

An improved hydraulic cement and resultant hydraulic cement composition having an imidized acrylic polymer uniformly distributed therein.

BACKGROUND OF THE INVENTION

The present invention is directed to an improved hydraulic cement and toa hydraulic cement composition having therein the subjectimproved-cement. Specifically, the present invention relates to animproved hydraulic cement composed of a mixture of an imidized acrylicpolymer, as fully described below and hydraulic cement and to hydrauliccement compositions such as mortars and concrete which is capable ofimparting high flowability to said compositions and of causing thetreated composition to retain high flowability over a sustained periodof time without imparting a significant delay in the initial set timefor the composition.

Although increased flowability can be attained by using large dosages ofwater in a hydrating cement composition, it is well known that theresultant cement based structure will have poor compressive strength andrelated properties. Various additives have been proposed to increase theflowability (known as "slump") to cement composition, such as mortar andconcrete compositions, without increasing the water content of theinitially formed composition. Such additives have been classified as"cement superplasticizers" and include, for example, compounds, such asnaphthalene sulfonate-formaldehyde condensates lignin sulfonates and thelike.

More recently, copolymers of alkenyl-ethers and acrylic acid or maleicanhydride, and derivatives thereof, have been proposed as agentssuitable to enhance slump [Japanese Patent Publication (Kokai) Nos285140/88 and 163108/90]. Further, copolymers formed from thecopolymerization of hydroxy-terminated allyether and maleic anhydride orthe allyether and a salt, ester or amide derivative of maleic anhydridesuch as disclosed in U.S. Pat. No. 4,471,100 have been proposed ascement admixtures capable of enhancing slump.

In each of the above instances, the proposed cement admixture materialwhen used in a cement composition does not provide the desiredcombination of properties or only provide them in low degrees. Forexample, esterified acrylate copolymers, while providing good slumpenhancement, also causes the treated cement composition to exhibitexcessive set retardation.

It is highly desired to have an admixture for cement compositions whichis capable of imparting to the treated composition, a high degree ofslump, of preventing a decrease in slump (decrease in flowability) overa sustained period of time, and at the same time, not causing thecomposition to exhibit excessive set retardation.

SUMMARY OF THE INVENTION

The present invention is directed to an improved hydraulic cement and tocement composition formed with said cement, wherein the cement containsan imidized acrylic polymer or copolymers thereof. The polymer can berepresented by the general formula ##STR1## wherein each R independentlyrepresents hydrogen atom or a methyl (CH₃ --) group; A represents ahydrogen atom, a C₁ -C₁₀ alkyl group, R' or an alkali or alkaline earthmetal cation or a mixture thereof; R' represents a hydrogen atom or a C₂-C₁₀ (preferably C₂ -C₄) oxyalkylene group (BO) or a plurality (1-200,preferably from 1 to 70) of said groups which is terminated with a C₁-C₁₀ alkyl group (R") or mixtures thereof; and a, b, c, and d representmolar percentages of the polymer's structure such that a has a value ofabout 50 to 70; the sum of c plus d is at least 2 to a value of (100-a)and is preferably from 3 to 10; and b is not more than [100-(a+c+d)].

Cement compositions formed with the improved cement of the presentinvention have been unexpectedly found to exhibit a high degree of slumpover a sustained period of time while not having any significant setretardation.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to an improved cement and to cementcompositions formed with said cement. The presently described improvedcement has been unexpectedly found to provide a cement composition, suchas mortar or concrete, having high flowability over an extended periodof time without imparting a significant delay in the initial set time ofthe composition. Thus the presently achieved cement compositions arecapable of being readily formed into a desired shape, having substantialself-leveling properties and can be worked over an extended period fromcommencement of hydration. At the same time, the present cementcomposition does not exhibit extensive delay in set and, therefore, doesnot delay the timetable for forming the desired structure.

The improved cement of the present invention is composed of asubstantially uniform mixture of an imidized acrylic polymer, as fullydescribed below, and a hydraulic cement. The cement can be selected fromany conventional hydraulic cement such as, for example, normal portlandcement (meeting the requirements of ASTM C-150), high early strengthportland cement, ultra high early strength portland cement,blast-furnace slag cement, fly-ash cement, blended portland cements,calcium aluminate cements, calcium sulfate cements, magnesium phosphatecements and the like.

Imidized acrylic polymers have been unexpectedly found to enhance thecement and provide an improved product. The polymer which is imidized isan acrylic polymer The term "acrylic polymer", as used herein and in theappended claims is a homopolymer or copolymer of acrylic acid,methacrylic acid, their alkali metal salts as well as their C₁ -C₃₀alkyl esters. In addition, the acrylic polymer reactant and theresultant imidized acrylic polymer may contain units derived from othersingly and doubly ethylenically unsaturated monomers, such as styrene,alpha-methylstyrene, sulfonated styrene, maleic acid, acrylonitrile,butadiene and the like. Such other ethylenically unsaturated monomerderived units, when present, can be present in the subject polymer inamount of up to about 20 (preferably, up to about 10) weight percent ofthe total polymer provided that the resultant imidized acrylic polymeris water soluble. Such other ethylenically unsaturated monomer derivedunits, although not shown in the structural formula exemplifying thesubject imidized acrylic polymer, are contemplated to optionally be apart thereof.

The acrylic polymer found useful herein are low molecular weightpolymers which are soluble in polar solvents such as water. They shouldbe selected so that the resultant imidized acrylic polymer has a numberaverage-molecular weight of from about 1,000 to 100,000, preferably fromabout 1,500 to 20,000. Acrylic polymers of both homopolymer andcopolymer character, are formed by conventional free radicalpolymerization and are commercially available.

The imidized acrylic polymer is formed by reacting an acrylic polymerwith ammonia or an alkoxylated amine. When an alkoxylated amine is usedas a reactant, the imidization may be carried out neat, as the acrylicpolymers are soluble in the amines. It is preferred to commence theimidization in the presence of small amounts of water.

The amine reactant useful in forming the desired imidized acrylicpolymer can be selected from ammonia or an alkyl-terminated alkoxy aminerepresented by the formula:

    H.sub.2 N-(BO).sub.n -R"

in which BO represents a C₂ -C₁₀ (preferably a C₂ -C₄) oxyalkylene groupin which O represents an oxygen atom and B represents a C₂ -C₁₀(preferably C₂ -C₄) alkylene group or mixture; and R" represents a C₁-C₁₀ (preferably C₁ -C₄) alkyl group and n is an integer selected from 1to 200 preferably from 1 to 70.

The acrylic polymer and amine reactant form the desired imidized acrylicpolymer by heating the reactants either in an aqueous solution or neatat elevated temperatures of from about 150° C. to 250° C. preferablyfrom 170° C. to 200° C. under ambient pressure or, under a pressurelower than ambient pressure. Further, when the reaction is carried outunder ambient or substantially ambient pressure it is preferred toconduct the reaction while passing air or nitrogen gas over the liquidreaction medium or by bubbling the gas through the medium to removewater and other low molecular weight by-products from the reaction zone.

The amine reactant is normally used in from about 5 to 90 mol percentand preferably from 10 to 20 mol percent based on the acrylic acid unitspresent in the acrylic polymer.

The imidization reaction can be enhanced by conducting the reaction inthe presence of a basic catalyst, an acid catalyst and/or atransamidation catalyst. Such catalysts may be selected from a tertiaryamine, such as dicyclohexyl-amine, 1,1,3,3-tetramethylguanidine,1,3-diphenylguanidine, quinoline, isoquinoline, 4-benzylpyridine,4-phenylpyridine, 2,3-benzodiazine, 1,4-benzodiazine, 1-benzazine,1,3-benzodiazine, N,N'-dicyclohexyl-carbodiimide, 2,2'-bipyridyl,2,3'-bipyridyl, 2,4'-bipyridyl or such catalyst can be selected from thegroup consisting of HCl, Sb₂ O₃, Ti-(OC₄ H₉)₄, NaNH₂, SnO₂, potassium orsodium alkoxides, manganese acetate, and so forth. The catalyst can bepresent in amounts of from 0.1 to 5 weight percent based on the aminereactant.

The reactants are contacted with each other at the above describedreaction conditions-for from about 1 to 8 hours and preferably fromabout 1.5 to 2.5 hours. During the course of the reaction, water (aby-product) is removed to drive the reaction to imidization.

Other known methods of imidization can be used provided the resultantpolymer is of the molecular weight and degree of imidization and othercharacteristics, as described herein.

The imidized acrylic polymer found useful in the present invention,which may be formed in the manner described above, has a structuralformula of: ##STR2## wherein each R independently represents hydrogenatom or a methyl (CH₃ --) group; A represents a hydrogen atom, a C₁ -C₁₀alkyl group, R' or an alkali or alkaline earth metal cation or a mixturethereof; R' represents a hydrogen atom or a C₂ -C₁₀ (preferably C₂ -C₄)oxyalkylene group (BO) or a plurality (1-200, preferably from 1 to 70)of said groups which is terminated with a C₁ -C₁₀ alkyl group (R") ormixtures thereof; and a, b, c, and d represent molar percentages of thepolymer's structure such that a has a value of about 50 to 70; the sumof c plus d is at least 2 to a value of (100-a) and is preferably from 3to 10; and b is not more than [100-(a+c+d)].

The preferred imidized polymer is represented by the above formula inwhich A is a hydrogen atom or an alkali metal cation; R' is at leastfrom 50 to 90 weight percent of the polymer and comprisespolyoxyethylene or polyoxypropylene units or mixtures thereof. Furtherit is preferred that a is a numerical value of from 60-70, and the sumof c and d is a numerical value of at least 3 (preferably at least 5) tothe value of (100-a).

The imidized acrylic polymer is normally a high-boiling viscous liquidwhich is substantially soluble in water. In most instances, the polymeris soluble in all proportions.

The improved cement of the present invention is composed of asubstantially uniform mixture of the hydraulic cement and the imidizedacrylic polymer which polymer should be present in from 0.005 to 5(preferably from 0.03 to 1 and most preferably from 0.05 to 0.3) weightpercent based on the weight of hydraulic cement. In order to aid informing the uniform mixture, the imidized acrylic polymer can be mixedwith the cement as an aqueous solution having from about 30 to 50 weightpercent imidized acrylic polymer solids in the solution.

The imidized acrylic polymer treated cement can be formed at any stageof the cement's formation or use. For example, the polymer can be mixedat the cement mill with clinker cement raw material during its grindingto form cement powder. It can also be applied to the cement powderduring its blending with other dry materials to prepare a specific typeof cement, such as blended cement, pozzolanic cement and the like.

Alternately, the improved cement can be formed in situ during the courseof preparing a cement composition such as a mortar mix (hydrauliccement, sand and water) or a concrete (hydraulic cement, sand, largeaggregate, such as stone, and water). The instant imidized acrylicpolymer can be added (conventionally as a aqueous solution) as part ofthe water of hydration or can be added separately. In the later methodof application, the water of the aqueous polymer solution should becalculated as part of the total water content of the cement composition.

As stated above, the imidized acrylic polymer of the improved cement(whether as a dry blend of cement and polymer or as formed in situ aspart of the formation of a wet unset cement composition) should be from0.005 to 5, preferably from 0.03 to 1 and most preferably from 0.05 to0.3 weight percent of solid imidized acrylic polymer based on the weightof solid hydraulic cement of the cement composition.

Cement compositions formed with the present improved cement have asignificantly higher degree of flowability (higher degree of slump),than compositions formed with conventional hydraulic cement. Further,the present cement compositions are capable of retaining their highdegree of slump over a sustained period of time giving the artisan anextended period to work the cement composition into its final shape.Finally, the present cement composition achieves initial set withoutexhibiting excessive retardation. Thus, the use of this cementcomposition does not cause delay of the working time required to form aparticular structure.

Conventional cement additives, such as air entrainers, water proofingagents, strength enhancers, corrosion inhibitors, antifoaming agents andcuring accelerators can be used with the subject cement additive. Theseadditives can be mixed with the cement composition prior to, along withor subsequent to the addition of the present cement additive.

The present invention is further explained by the following exampleswhich are given for illustrative purposes only and are not meant tolimit the invention, as defined by the claims, appended hereto. Allparts and percentages are by weight unless otherwise stated.

EXAMPLES EXAMPLE 1

40 parts of solid polyacrylic acid of 5000 molecular weight was added to60 parts of a polyethylene--polypropylene oxide polymer of molecularweight 700 which is terminated at one end with a primary amine group andat the other end by a methyl group. The reaction mixture was stirred for30 minutes at ambient temperature followed by 1 hour and 10 minutes at180° C. under a blanket of flowing nitrogen gas. The water by-productwas removed in the nitrogen gas stream. The resultant product was aviscous amber liquid. The liquid was analyzed by infrared spectroscopyand the resultant spectra had peaks at 1720 cm⁻¹, 1630 cm⁻¹ and 750cm⁻¹, which indicates the presence of imide groups. This liquid was alsoanalyzed by conductiometric titration and the nitrogen linkages werefound to have an 4:1 amide:imide group ratio.

EXAMPLE 2

7.5 parts of solid polyacrylic acid of 2000 molecular weight wasdissolved in 7.7 parts deionized water. To this resultant solution wasadded 52.1 parts of a polyethylene-polypropylene oxide polymer ofmolecular weight 2000 which was terminated at one end by a primary aminegroup and at the other end by a methyl group. The mixture was heated andmaintained at 180° C. under a flowing nitrogen gas blanket for a totalof 2 hours to remove the water of solution and that formed as a reactionby-product. The resulting product was an amber viscous liquid.

EXAMPLE 3

25 parts of a 50% aqueous solution of a polyacrylic acid of 5000molecular weight was combined with 52 parts of apolyethylene-polypropylene oxide polymer of molecular weight 2000 whichwas terminated at one end by a primary amine group and at the other endby a methyl group. The mixture was heated and maintained at 180° C.while under flowing nitrogen gas stream for a total of 2 hours. Thewater of solution and formed as by-product was removed in the nitrogengas stream. The resulting product was an amber viscous liquid.

EXAMPLE 4

30 parts of a 65% aqueous solution of a polyacrylic acid of 2000molecular weight was mixed with 29.3 parts of a(polyethylene-polypropylene) oxide polymer of molecular weight 700 whichwas terminated at one end by a primary amine group and at the other endby a methyl group. The mixture was heated under flowing blanket ofnitrogen gas at 180° C. for 1 hour and 30 minutes. The water of thesolution and from the reaction was removed by the nitrogen gas stream.The resulting product was an amber viscous liquid.

EXAMPLE 5

19.2 parts of a 65% aqueous solution of a polyacrylic acid of 2000molecular weight was combined with 3.0 parts of 30% aqueous solution ofammonia. To the solution was then added 48 parts of apolyethylene-polypropylene oxide polymer of molecular weight 700 whichwas terminated at one end by a primary amine group and at the other endby a methyl group. The mixture was heated and maintained at 180° C.while under flowing nitrogen gas stream for a total of 30 minutes. Thewater of the solution and that formed as a by-product was removed in thenitrogen stream. A yellow creamy liquid was isolated as the product andwas determined to contain both reacted ammonia and alkoxyamine groups.

EXAMPLE 6

154 parts of a 50% solution in water of polyacrylic acid of 2000molecular weight was added to 312 parts of a polyethylene-polypropyleneoxide polymer of molecular weight 2000 which was terminated at one endby a primary amine group at the other end by a methyl group. The mixturewas heated and maintained at 180° C. under flowing nitrogen gas streamfor a total of 7 hours until substantially all of the water was removed.The resulting product was an amber viscous liquid.

EXAMPLE 7

5.2 parts of a polymethacyrlic acid of molecular weight 3400 wasdissolved in 8.2 parts of distilled water. After 45 minutes, thepolymethacrylic acid was completely dissolved and 18.0 parts of apolyethylene-polypropylene oxide polymer of molecular weight 2000terminated at one end by a primary amine and terminated at the other endby a methyl group was added. The mixture was stirred at room temperaturefor 30 minutes. Heat was applied at 180° C. under flowing nitrogen for 1hour. The resulting product was an amber viscous liquid.

A sample of the resultant imidized acrylic polymer was tested as part ofan ordinary portland cement mortar in a method based on JapaneseIndustrial Standard (JIS) A6204. A sand/cement/water ratio of 1/3/0.50was used with the polymer dissolved in the water to give a dosage of0.15% solid polymer based on solid cement (s/s). In order to eliminatethe effects of air on the flow of the mortar, a commercial defoamer wasemployed at 20-30 ppm based on the weight of cement. Set times weremeasured using an automated penetrometer on a sample formed using 0.20%s/s dosage of polymer. Results of these tests are given in Table 3below.

EXAMPLE 8

Each of the formed imidized acrylic polymers of Examples 1,3,4,5 and 6were formed into 50% aqueous solutions with deionized water. Each of thesolutions was used in forming a cement composition composed of standardhydraulic portland cement and water. The polymer to cement weight ratio(solid polymer/solid cement, s/s) was 0.002 and the water to cementratio was 0.5. A miniature slump test developed by Kantro as describedin "Cement, Concrete and Aggregates"' Vol. 2, No. 2, Page 95 1980 wasused to measure slump of each sample. Set was measured by an automatedpenetrometer. The results for samples of Examples 2-6 are given in Table1 below. Further, samples of a concrete cement composition were treatedwith the imidized acrylic polymer of Example 6 and, for comparativepurposes, with a conventional-concrete superplasticizing agent,naphthalene sulfonate formaldehyde condensate ("NSFC"), in dosages setforth in Table 2 below. The concrete mix design was composed of:portland cement at a rate of 600 lbs/yd³ ; sand at a rate of 1400lbs/yd³ ; coarse aggregate (crushed stone) at a rate of 1700 lbs/yd³ andwater (including from admixture) in 300 lbs/yd³. These samples and ablank were tested according to ASTM C143 for slump, ASTM C403 for set,and ASTM C39 for compressive strength. A commercial defoamer was alsoincorporated to eliminate air effects on slump and compressive strength.The results of these tests are given in Table 2 below.

                  TABLE 1                                                         ______________________________________                                        Cement Paste Results                                                          Minislump spread (cm)                                                                 Dosage  9      18   30   45   60    Set time                          Preparation                                                                           (% s/s) min.   min. min. min. min.  (min.)                            ______________________________________                                        Blank   --      14.9   13.9 12.6 10.9 10.0  187                               Example 2                                                                             0.2     19.8   20.4 20.0 19.3 18.3  327                               Example 3                                                                             0.2     20.7   24.4 22.3 20.4 18.4  334                               Example 4                                                                             0.2     18.1   18.5 18.8 17.5 16.5  342                               Example 5                                                                             0.2     18.7   20.2 17.6 17.5 16.6  288                               Example 6                                                                             0.2     21.6   20.9 22.0 18.9 18.9  287                               ______________________________________                                    

                                      TABLE 2                                     __________________________________________________________________________    Concrete Results                                                                                                Compressive                                 Dosage    Slump                   Strength                                          (%  (in. at                                                                           (in. at                                                                            (in. at                                                                            (in. at                                                                            Set  1 day                                                                             7 day                                                                             28 day                              Preparation                                                                         s/s)                                                                              9 min.)                                                                           18 min.)                                                                           30 min.)                                                                           45 min.)                                                                           (hr:min)                                                                           (psi)                                                                             (psi)                                                                             (psi)                               __________________________________________________________________________    Blank --  2.75                                                                              NM   NM   NM   4:20 1782                                                                              5140                                                                              6097                                Example 6                                                                           0.125                                                                             8.00                                                                              7.25 5.25 3.00 4:14 2012                                                                              5182                                                                              6442                                NSFC  1.00                                                                              8.00                                                                              5.50 3.25 2.50 5:23 1683                                                                              3641                                                                              5872                                __________________________________________________________________________

The results of Table 2 clearly show that the present imidized acrylicpolymer admixture containing cement composition provides a high initialslump, retains a high slump over a sustained period, has substantiallyno set retardation and exhibits enhanced compressive strength whencompared to the untreated cement composition and to a cement compositioncontaining a conventional superplasticizer, NSFC.

                  TABLE 3                                                         ______________________________________                                        Mortar Flow Results                                                           Flow                                                                                  Dosage   4 min.   30 min.                                                                              60 min.                                                                              Set.sup.1                             Preparation                                                                           (% s/s)  (mm)     (mm)   (mm)   (hr:min)                              ______________________________________                                        Blank   --       105      NM     NM     5:00                                  Example 7                                                                             0.15     220      197    163    5:30                                  ______________________________________                                         .sup.1 Set measured at 0.20% s/s of Example 7.                           

What is claimed:
 1. An improved cement comprising a mixture of ahydraulic cement and from 0.01 to 2 weight percent based on the weightof said hydraulic cement of an imidized acrylic polymer represented bythe structure of: ##STR3## wherein each R independently represents ahydrogen atom or a methyl (CH₃ --) group; A represents hydrogen atom, aC₁ -C₁₀ alkyl group, R' or an alkali metal cation or a mixture thereof;R' represents a hydrogen atom or a C₂ -C₁₀ oxyalkylene group representedby (BO)_(n) R" in which O represents an oxygen atom, B represents a C₂-C₁₀ alkylene group, R" represents a C₁ -C₁₀ alkyl and n represents aninteger of from 1-200, or mixtures thereof; and a, b, c and d arenumerical values representing molar percentage of the polymer'sstructure such that a is a value of about 50 to 70; the sum of c+d is avalue of from about 2 to the numerical value of (100-a); and b is aremainder value of [100-(a+c+d)].
 2. The improved cement of claim 1wherein B represents a C₂ -C₃ alkylene group or mixture thereof and R"represents a C₁ -C₃ alkyl group.
 3. The improve cement of claim 1wherein R' represents hydrogen atom.
 4. The improved cement of claim 1wherein R' represents a chain represented by (BO)_(n) R" in which Orepresents an oxygen atom, B represents a C₂ -C₃ alkylene group ormixture of said groups and R" represents a C₁ -C₃ alkyl group and nrepresents an integer of from 1 to
 70. 5. The improved cement of claim 1wherein a represents an integer of 60-70 and the sum of c+d is aninteger of at least 5 to the numerical value of (100-a).
 6. The improvedcement of claim 5 wherein R' represents a plurality of from 1 to 70units of oxyalkylene groups terminated with a C₁ -C₃ alkyl group.
 7. Inan improved composition comprising a mortar formed from a mixture of ahydraulic cement, sand and water or a concrete formed from a mixture ofhydraulic cement, sand, large aggregate and water, wherein theimprovement comprises utilizing a hydraulic cement of claim
 1. 8. In animproved composition comprising a mortar formed from a mixture of ahydraulic cement, sand and water or a concrete formed from a mixture ofhydraulic cement, sand, large aggregate and water, wherein theimprovement comprises utilizing a hydraulic cement of claim
 2. 9. In animproved composition comprising a mortar formed from a mixture of ahydraulic cement, sand and water or a concrete formed from a mixture ofhydraulic cement, sand, larger aggregate and water, wherein theimprovement comprises utilizing a hydraulic cement of claim
 3. 10. In animproved composition comprising a mortar formed from a mixture of ahydraulic cement, sand and water or a concrete formed from a mixture ofhydraulic cement, sand, large aggregate and water, wherein theimprovement comprises utilizing a hydraulic cement of claim
 4. 11. In animproved composition comprising a mortar formed from a mixture of ahydraulic cement, sand and water or a concrete formed from a mixture ofhydraulic cement, sand, large aggregate and water, wherein theimprovement comprises utilizing a hydraulic cement of claim
 5. 12. In animproved composition comprising a mortar formed from a mixture of ahydraulic cement, sand and water or a concrete formed from a mixture ofhydraulic cement, sand, large aggregate and water, wherein theimprovement comprises utilizing a hydraulic cement of claim 6.